APPARATUS FOR MAKING JELLY TEST
Another apparatus that has been found accurate and practical is the device illustrated on the next page. It consists of a pressure tube (A), over the mouth of which is stretched a thin rubber diaphragm (B). The tube connects to a rubber bulb (M) and to a pressure gauge, or manometer (E) with a scale (F). The pressure tube is filled with water to the point (C). The manometer tubes also contain water. A three-way stop-cock (D) connects the tubes either to the bulb (M), or to the air, depending on the position. Below the pressure tube is a brass table (G), on which is placed the glass containing the glue-jelly to be tested.
Apparatus for Testing Jelly-Strength of Glue.
When the glass is in position, the table is raised by means of a threaded wheel until the glue surface forces the water resting on the flexible diaphragm up to the fixed mark L. Then the stop-cock is turned to connect the pressure tube and gauge to the rubber bulb. By pressing the bulb the water is forced down in the pressure tube and so expands the diaphragm into the jelly, the liquid in the gauge rising simultaneously. Pressure on the bulb is continued until the water reaches the mark N.
Thereupon the stop-cock is again turned, the water is held at the point N, and the pressure is indicated by the height of the liquid in the gauge. The degree of pressure is the measure of the consistency of the glue-jelly.
The initial contact between the jelly and the rubber diaphragm is always the same, all jellies therefore having the same initial pressure. When the diaphragm is forced down into the jelly, the pressure required depends entirely upon the resistance that the jelly offers. The slightest difference in the consistencies of the various jellies will alter the pressure required, the differences being accurately recorded by the gauge upon the scale.
Advantages of this apparatus are that the relative value of the jelly compared with the standard is expressed in concrete figures; the method of operation is simple; and the instrument is so sensitive that it will record a change in reading between two samples of glue in which a difference of ¹⁄₁₀₀th ounce of dry glue is used. Repeated tests may be made on the same jelly, as the surface is not broken. With a little practice a single glue may be tested in twenty seconds, or less.